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"It's still too early to say the Sites Complex fires are suspicious. However, five separate fires all along the roadway do have investigators looking into whether or not they were human-caused," Berlant told KCRA 3's Mike TeSelle.

The Sites Complex fire, near the farming community of Maxwell, has consumed about 4,200 acres so far.

It was 60 percent contained as of Tuesday evening -- two days after it started.

State fire officials expect to have the fire fully contained by the weekend.

State fire officials also say the blaze began as five separate fires. Three of those fires were contained and the remaining two have burned together.

Although the fire came close to a few ranches, no structures are currently threatened. More than 1,000 firefighters are working on the blaze.

Berlant said winds have died down.

But crews will still have to deal with high temperatures and dry conditions.

"It's very steep terrain, and very hot conditions. Staying hydrated is important. The main thing working against them right now is the weather," said Kirk Van Wormer, a battalion chief. "The heat fatigues you very quickly."

A strike team from Humboldt county arrived in Colusa county shortly after 8 a.m. to work a section of the grass fire in Colusa county.

Crews said the heat is something they train for but it is still difficult to deal with.

"It wears you down over a course of time," said Cal Fire Firefighter David Tikkanen.

Van Wormer said Cal Fire is receiving help from several local agencies including Colusa Yolo, Sutter, Yuba and Glenn counties.

The Mill Fire in the Mendocino National Forest was 20 percent contained and has so far cost $1.2 million to contain.

Officials have issued an air quality advisory due to smoke in the area as more than 700 firefighters are battling the blaze in rugged terrain near Letts Lake. The flames have already forced the closure of campgrounds and the evacuation of a handful of homes.